It is known, for the purpose of cleaning planar window glazing in tower blocks, to mount an elongate brush to be rotatable about its axis between end mountings movable in synchronism between one end of a path of movement and the other, so that in use the brush is applied over a rectangular area. One example of apparatus for cleaning tower block window glazing is described in U.K. Patent Specification No. 1154983, from which it is readily apparent that this known apparatus is clearly not suited to cleaning non-planar glazed roof structures, for example of the atrium-type or the barrel arch-type.